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Climate model simulations of the PETM (Paleocene-Eocene Thermal Maximum) warming have mainly focused on replicating the global thermal response through greenhouse forcing, i.e. CO2, at levels compatible with observations. Comparatively less effort has gone into assessing the skill of models to replicate the response of the hydrologic cycle to the warming, particularly on regional scales. Here we have assembled proxy records of regional precipitation, focusing on the Mid-Atlantic Coasts of North America (New Jersey) and Europe (Spain) to test the response of the hydrologic system to greenhouse gas forcing of the magnitude estimated for the PETM (i.e., 2×). Given evidence that the PETM initiated during a maximum in eccentricity, this includes the response under neutral and extreme orbital configurations. Modeled results show excellent agreement with observations in Northern Spain, with a significant increase in both mean annual and extreme precipitation resulting from increased CO2 levels under a neutral orbit. The Mid Atlantic Coast simulations agree with observations showing increases in both overall and extreme precipitation as a result of CO2 increases. In particular, the development of sustained atmospheric rivers might be significantly contributing to the extremes of the eastern Atlantic, whereas extratropical cyclones are likely contributing to the extremes in the western Atlantic. With an eccentric orbit that maximizes insolation during boreal summer, there is a suppression of extreme precipitation events in the eastern Atlantic and an amplification in the western Atlantic, which may account for observations in the relative timing of the sedimentary response to the carbon isotope excursion associated with the PETM.

Rapid carbon input into the ocean–atmosphere system caused a dramatic shoaling of the lysocline during the Paleocene–Eocene thermal maximum (PETM), a transient (∼ 170 kyr) global warming event that occurred roughly 55 Ma. Carbon cycle models invoking an accelerated carbonate–silicate feedback mechanism to neutralize ocean acidification predict that the lysocline would subsequently deepen to depths below its original position as the marine carbonate system recovered from such a perturbation. To test this hypothesis, records of carbonate sedimentation and preservation for PETM sections in the Weddell Sea (ODP Site 690) and along the Walvis Ridge depth transect (ODP Sites 1262, 1263, and 1266) were assembled within the context of a unified chronostratigraphy. The meridional gradient of undersaturation delimited by these records shows that dissolution was more severe in the subtropical South Atlantic than in the Weddell Sea during the PETM, a spatiotemporal pattern inconsistent with the view that Atlantic overturning circulation underwent a transient reversal. Deepening of the lysocline following its initial ascent is signaled by increases in %CaCO3 and coarse-fraction content at all sites. Carbonate preservation during the recovery period is appreciably better than that seen prior to carbon input with carbonate sedimentation becoming remarkably uniform over a broad spectrum of geographic and bathymetric settings. These congruent patterns of carbonate sedimentation confirm that the lysocline was suppressed below the depth it occupied prior to carbon input, and are consistent with the view that an accelerated carbonate–silicate geochemical cycle played an important role in arresting PETM conditions.

Paleocene–Eocene warming and changes in oceanic hydrography should have significantly impacted the ecology of marine microorganisms, both at the surface and on the seafloor. We analyzed several key characteristics of foraminifera from two Shatsky Rise (ODP Leg 198) cores spanning the P/E boundary including the maximum test diameters of the largest calcareous trochospiral benthic foraminifera and largest shallow-dwelling planktonic foraminifera, and the stable carbon and oxygen isotope ratios of benthic foraminifera and bulk samples. We also qualitatively constrained changes in bottom water dissolved oxygen concentrations by quantifying changes in benthic species abundances. We find warming synchronous with an unusual increase in the size of surface-water planktonic in contrast to deep-water benthic foraminifera which decrease in size. We suggest that a decline in bottom water dissolved oxygen is the primary mechanism responsible for the size reduction of Pacific deep-sea benthic foraminifera, whereas the contemporaneous size increase of surface-water planktonic foraminifera is attributed to an increase in thermal stratification and decrease in local nutrient supply.

The earliest Oligocene (∼33.5 Ma) is marked by a major step in the long-term transition from an ice-free to glaciated world. The transition, characterized by both cooling and ice-sheet growth, triggered a transient but extreme glacial period designated Oi-1. High-resolution isotope records suggest that Oi-1 lasted for roughly 400,000 yr (the duration of magnetochron 13N) before partially abating, and that it was accompanied by an ocean-wide carbon isotope anomaly of ∼0.75‰. One hypothesis relates the carbon isotope anomaly to enhanced export production brought about by climate-induced intensification of wind stress and upwelling, particularly in the Southern Ocean. To understand how this climatic event affected export production in the Southern Ocean, biogenic silica (opal) and carbonate accumulation rates were computed for the sub-polar Indian Ocean using deep-sea cores from ODP Site 744, Kerguelen Plateau. Our findings suggest that net productivity in this region increased by several fold in response to the Oi-1 glaciation. In addition, calcareous primary producers dominant in the Late Eocene were partially replaced by opaline organisms suggesting a trend toward seasonally greater surface divergence and upwelling in this sector of the Southern Ocean. We attribute these changes to intensification of atmospheric/oceanic circulation brought about by high-latitude cooling and the appearance of a full-scale continental ice-sheet on East Antarctica. Higher terrigenous sediment accumulation rates support the idea that wind-induced changes in regional productivity were augmented by an increased supply of glacial dust and debris that provided limiting micro-nutrients (e.g., iron-rich dust particles). We speculate that the rapid changes in biogenic sediment accumulation in the Southern Ocean and other upwelling-dominated regions contributed to the ocean-wide positive carbon isotope anomaly by temporarily increasing the burial rate of organic carbon relative to carbonate carbon. The changes in burial rates, in turn, may have produced a positive feedback on climate by briefly drawing down atmospheric pCO2.

Study of planktonic foraminiferal assemblages preserved in the central, equatorial Pacific (ODP Site 865) reveal that genera which inhabited the near-surface, mixed layer diversified during the latest Paleocene thermal maximum (LPTM). This transient diversification gave rise to a suite of short-lived (50 to several 100 ka), distinctive morphotypes (Morozovella allisonensis sp. nov., M. africana, and Acarinina sibaiyaensis) that are restricted to the LPTM interval. Parallel morphometric and stable isotopic data have been recorded from individual shells of members of the M. velascoensis/M. allisonensis and A. soldadoensis/A. sibaiyaensis lineages. The single-specimen isotope data confirm that M. allisonensis and A. sibaiyaensis are indeed stratigraphically restricted to the LPTM carbon isotope excursion; all specimens recorded anomalously low δ13C values. A stratigraphic succession of single-specimen isotope data from within the δ13C excursion interval was used to reconstruct the complex population dynamics which mediated the rapid (

Climatic warming from the late Paleocene into the early Eocene had profound effects on atmospheric and marine circulation, marine thermal gradients, and benthic biota. In addition, marine carbon isotope values decreased substantially in both surface and deep waters. Because carbon is rapidly exchanged between reservoirs at the earth's surface, such as marine surface water, the atmosphere, land plants, and materials that obtain carbon from plants (e.g., soil minerals and herbivores), carbon isotope fluctuations provide time lines linking the marine and continental records. We analyzed the carbon isotope composition of paleosol carbonates and mammalian tooth enamel from stratigraphic sections in northwestern Wyoming. Carbon isotope correlation demonstrates that a short interval of extreme high-latitude warming coincided precisely with the first appearance of several important modern mammalian orders. In addition, oxygen isotope analyses of fossils and paleosol carbonates provide information about climatic conditions on land in the Paleogene. We reconstructed the oxygen isotope composition of local meteoric water using biogenic minerals. Paleocene-Eocene meteoric water was significantly 18 O-depleted, indicating substantial loss of water vapor during its transport to the region. Soil temperature was calculated as a proxy for mean annual temperature, assuming oxygen isotope equilibrium between soil carbonate and meteoric water. Calculated temperatures were plausible (≈10–25°C), but highly variable, prohibiting high-resolution analysis of local temperature variations in response to global climatic warming.

Rea, D. K., Zachos, J. C., Owen, R. M. and Gingerich, P. D., 1990. Global change at the Paleocene-Eocene boundary: climatic and evolutionary consequences of tectonic events. Palaeogeogr., Palaeoclimatol., Palaeoecol., 79: 117-128. Events of the Paleocene-Eocene boundary provide the clearest example to date of how a tectonic event may have global climatic consequences. Recent advances permit well-constrained stratigraphic determination of several events that occurred at that boundary, in chron C24R: a many-fold increase in sea-floor hydrothermal activity, a global warming, a reduction in the intensity of atmospheric circulation, a conversion to salinity-driven deep ocean circulation, a marked lightening of oceanic 313C values, extinction and evolution of both benthic foraminifera and land mammals, and important plate-boundary reorganizations including the outpouring of the east Greenland volcanics and the initiation of the oceanic rift between Norway and Greenland. We hypothesize that enhanced sea-floor hydrothermal activity occasioned by global tectonism resulted in a flooding of the atmosphere with COz, causing a reduced pole-to-equator temperature gradient and increased evaporation at low latitudes. Increased formation of warm, salty, probably low-nutrient waters coupled with the warm temperatures at high latitudes occasioned a salinity-driven, rather than temperature-driven, deep-water circulation. This newly-evolved ocean circulation pattern changed the apportionment of global heat transport from the atmosphere to the ocean, with concomitant changes in the circulation intensity of both. Reduced intensity of atmospheric circulation resulted in lower oceanic biological productivity and enhanced seasonality of climate on the continents. A major extinction event among benthic foraminifera was probably a response to the new low-nutrient and chemically changed bottom waters, and endemism following rapid evolution and dispersal of mammalian orders may have been in response to the new continental climate regime.

The Cretaceous/Tertiary (K/T) boundary in southern Alabama occurs in a sequence of interbedded shallow-marine limestones and marls deposited during a Late Maastrichtian regression and subsequent Danian transgression. The presence of a diverse assemblage of Cretaceous and Paleocene benthic micro- and macrofossils has allowed detailed examination of paleoenvironmental changes in this shallow-marine setting at the time of the K/T boundary extinctions. Although extensive diagenesis has resulted in the recrystallization and cementation of whole rock carbonate, a few molluscan macrofossils have retained their original calcitic structure. The oxygen isotopic record of these macrofossils shows a gradual cooling of 2–3°C over a 3 m.y. period which began in the late Maastrichtian and continued into the Danian. The characteristic depletion in δ 13 C across the K/T boundary displayed by planktonic microfossils from pelagic sequences is not recorded at Braggs. Major changes in whole rock trace and minor element chemistry reflect the decrease in terrigenous mineral fluxes to this location brought about by the rapid Early Paleocene transgression.